Interpretive Summary: In the U. S., most broiler companies use ice water immersion to cool broiler carcasses during processing. In the E. U., cool air is commonly used to achieve the same end. Many broiler carcasses are contaminated with the human pathogen Campylobacter; it is unclear whether these two different carcass chilling methods affect Campylobacter in the same way. In this study, broiler carcasses were split into mirror image halves, one half was chilled in ice water and the other in cold air. The chilling methods were equally effective at lowering the carcass temperature to about 1.5 C. Total aerobic bacteria, E coli, coliforms and Campylobacter were enumerated on the carcass halves after each chilling procedure. Fewer of each type of bacteria were found on carcass halves chilled in ice water than on those chilled in cold air. Campylobacter from chilled carcass halves were collected and characterized by subtyping with pulsed field gel electrophoresis and antimicrobial resistance testing. Overall, no clear effect of chill method was observed on the population of Campylobacter. Most subtypes detected were found on carcass halves chilled by either method. Resistance to antimicrobial drugs was only noted in C. coli isolates from one replication; six isolates from air chilled carcasses and 3 isolates from water chilled carcasses were resistant to ciprofloxacin and nalidixic acid. Resistnace to other antimicrobials was not observed. Neither chill method appears to select for different populations of Campylobacter. This information will be useful to broiler processors. Since both chill methods appear to affect Campylobacter in the same way, the choice of method can be made based on the needs of each processor.

Technical Abstract:
Cold air or ice water can be used to chill poultry carcasses after slaughter. The objective of this study was to compare the effect of two chill methods on broiler carcass bacteria. Broiler carcasses were cut in half along the dorsal/ventral midline; one half was subjected to an ice water immersion chill in an agitated bath for 50 min while the reciprocal half was subjected to an air chill in a 1 C cold room for 150 min. Total aerobic bacteria, coliforms, E. coli and Campylobacter were enumerated from half carcass rinses. Species of Campylobacter isolates was determined by a commercial PCR method which was followed by molecular subtyping with PFGE and determination of antimicrobial susceptibility to nine drugs. Although significantly fewer of each bacterial type were detected per mL from immersion chilled carcasses than from air chilled carcasses, in each case the difference was less than 1 log 10 CFU/mL. Chilling method did not affect species, both Campylobacter jejuni and coli were recovered. Results of PFGE subtyping did not suggest that either chilling method selects for any specific subtypes; most subtypes were found on carcass halves used for both air and water immersion chill. Resistance to two antimicrobial drugs was noted in nine C. coli isolates, six from air chilled carcass halves and three from immersion chilled carcass halves. These data showed that immersion chilled carcasses have lower numbers of bacteria; however, the difference is not large and may be due to simple dilution. Both methods are effective for lowering carcass temperature and neither chilling method seems to select for specific species, subtypes or antimicrobial resistant Campylobacter.